1. Field of the Invention
The present invention relates to a P-type GaAs single crystal having low dislocation, and a manufacturing method therefor.
2. Related Arts
P-type GaAs single crystals have been widely used as sliced and epitaxially grown for use in manufacturing a compound semiconductor laser or a light-emitting diode (LED).
It is well known that the P-type GaAs single crystals widely used for compound semiconductor lasers and LEDs can be manufactured using various methods, such as the horizontal Bridgman (HB) method, the horizontal gradient freeze (GF) method, the liquid encapsulated crystal growth (LEC) method, the vertical Bridgman (VB) method, and the vertical gradient freeze (VGF) method.
Since high light emission efficiency and long service life are requisite qualities for a compound semiconductor laser, a P-type GaAs single crystal having a lower dislocation density is required. Therefore, generally, the horizontal Bridgman (HB) method, the gradient freeze (GF) method, the vertical Bridgman (VB) method, or the vertical gradient freeze (VGF) method is employed to manufacture a P-type GaAs single crystal.
However, when using any of these methods, the average dislocation density is equal to or greater than 1000 cm.sup.-2, and it is difficult to obtain a high yield when manufacturing P-type GaAs single crystals having an average dislocation density of 500 cm.sup.-2 or lower.
On the contrary, it is known that doping a crystal with S and Si can effectively reduce dislocation, However, in this case, only an N-type GaAs single crystal is obtained.
As example means for resolving the above shortcomings, doping GaAs crystal with Zn and S using the horizontal Bridgman (HB) method is described in Japanese Unexamined Patent Publication No. Sho 63-57079. However, although a P-type GaAs single crystal having an average dislocation density of 1000 cm.sup.-2 or lower can be obtained using this method, it is difficult to manufacture a P-type GaAs single crystal having an average dislocation density of 500 cm.sup.-2.
It has been reported that In, which is a neutral impurity, can contribute to the reduction of the dislocation of GaAs crystal (Proc. 12th Intern. Symp. on GaAs and Related Compounds, London-Bristol, 1986, p. 7-2). As related in this report, a 2-inch GaAs wafer which was doped with Zn, at a density of 1.5.times.10.sup.19 cm.sup.-3, and In, at a density of 4.0.times.10.sup.19 cm.sup.-3, served as a semiconductor wafer having no dislocation.
However, since the segregation coefficient of In is small, i.e., 0.1, in order to perform the high density doping of a crystal with In, a single crystal must be manufactured from melt-GaAs to which a large amount of In has been added in advance. However, if a crystal is manufactured under these conditions, cell growth is begun due to constitutional supercooling during the solidifying of the crystal, and there is a considerable reduction in productivity.